1. Field of the Invention
This invention relates to free radical polymerization processes employing chain transfer agents for controlling the molecular weight of polymer and copolymer produced.
2. Background of the Art
Techniques for controlling the molecular weight of polymer and copolymer with chain transfer agents are currently being developed. Problems associated with use of known chain transfer agents include undesirable odor, intense color, and broad molecular weight distribution in the resulting polymer. Improved chain transfer agents are of considerable interest to the chemical industry.
U.S. Pat. No. 2,383,425, issued to Stewart, discloses a class of complex compounds which are said to initiate and catalyze the polymerization of open-chain aliphatic conjugated dienes such as butadiene-1,3 either alone or in admixture with other copolymerizable materials. The complex compounds are defined as containing a central heavy atom and at least one nitrogen containing coordinating group connected to the heavy metal atom by a coordinating or secondary valence.
Enikolopyan et al., J. Poly. Sci., Polymer. Chem. Ed., 19: 879-889 (1981) disclose use of a cobalt complex of hematoporphyrin tetramethyl ether as catalysts for chain transfer to monomer. Each porphyrin molecule is said to cause not less than 2000 transfer reactions. Smirnov et al., Polymer Science, USSR, 23: 2807-2816 (1981) disclose the use of cobalt-porphyrin complexes as catalytic chain transfer agents for controlling molecular weight in the radical polymerization of styrene. Pashchenko et al., Doklady Akademii Nauk SSSR, 265(4): 889-892 (1982) disclose the use of a cobalt complex of etioporphyrin-I as a catalytic chain transfer agent for radical polymerization of methyl methacrylate. It has been found that one disadvantage of cobalt-porphyrin complexes is an intense color in resulting polymer.
U.S. Pat. No. 4,526,945, issued to Carlson and Abbey, disclose a process for the preparation of low molecular weight methacrylate polymers and copolymers. Methacrylate monomers and lower amounts of other ethylenically unsaturated monomers are polymerized in the presence of an azo or similar free radical catalyst in conjunction with between about 0.0001% and 0.01% by weight dimethylglyoxime pyridine complex of Cobalt(II). The resulting polymer exhibits controlled low molecular weight on the order of 500-20,000 as compared to about 100,000 in the absence of the cobalt(II) complex. The polymer is described as having improved color.
Takahashi et al., Bull. Chem. Soc. Jap., 36: 622-623 (1963) disclose the use of a cobalt cyanide complex in the presence of hydrogen as an initiator for the polymerization of methyl methacrylate, styrene, acrylonitrile, and butadiene.